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Increasing efficiency of conveyor belt J o transporting system 4 Belt Lonmin u r by G.G. le Roux* n a Paper written on project work carried out in partial fulfillment of BSc (Min. Eng.) degree l
P operating in an electrical interlocked system¹. a Currently reef and waste material are delivered p Synopsis to three of the conveyor belts from six different levels, one level at a time. e The purpose of the investigation was to assess various options for r increasing the efficiency of the conveyor belt transporting system The system is used for the transportation used at 4 Belt Shaft at Lonmin’s Marikana operations. The reason for of UG2 Reef, Merensky Reef and waste the investigation was to prevent the occurrence of a ‘bottleneck’ at material. UG2 reef and waste material are the main ore passes delivering ore to the conveyor belt system, thus delivered to the conveyor belt system through creating more fluent operational conditions. The options assessed for ore passes connecting the sub inclined shaft to increasing the efficiency of the conveyor belt transporting system all operating levels. Merensky Reef from all were: operating levels is delivered to the conveyor ➤ Variation of the conveyor speed belt system through one ore pass connecting ➤ Concurrent tipping from two ore passes on the belt all Merensky Reef levels to the sub inclined ➤ Increase the available drive unit power shaft. ➤ Increasing the feed rate from vibratory feeders ➤ Change in belt width/belt specifications Objective The report shows that the most preferable option to the current The objective of the project was to assess situation at 4 Belt, Lonmin, would be the option of concurrent tipping various options for increasing the efficiency of from two ore passes to the belt. the existing conveyor belt transporting system. The efficiency of the system needs to be increased due to an expected increase in mining production targets and to create more Introduction fluent operation conditions. At 4 Belt the shift time coincides for all During the period of December 2006 to levels of the mine, which leads to ore being January 2007, the author was allocated a trammed on all levels to the main ore passes at project in partial fulfillment of the BSC. Eng the same time. This results in a ‘bottleneck’, (Mining Engineering) degree. The project was when main ore passes from all levels of the given to the author by Lonmin and was mine are filled up at the same time². With the conducted at 4 Belt Shaft at Lonmin’s reef ore passes having a limited surge capacity Marikana operations. of ±250 tons of reef each, most of the reef ore passes have to be tipped more than once per Mine background day2. It often happens that the main ore pass 4 Belt is an underground platinum mine that is on a level is still filled up with rock by the time owned by Lonmin. The mine is situated in the the tramming team arrives at the ore pass with North West Province of South Africa near the next load of ore to tip. Rustenburg. Access to the mine workings is by The aim of the project was to create more means of an incline shaft and a sub incline fluent operation conditions for all levels by shaft. The inclination of both shafts is about either increasing the capacity of the belt twelve degrees measured from horizontal¹. The conveyor system or allowing concurrent mine was originally designed for the extraction feeding from more than one ore pass to the of only Merensky Reef but over the years other belt. reefs were identified such as the UG2 Reef. Therefore the mine produces two reefs at present, which is the Merensky Reef and the UG2 Reef. * University of the Witwatersrand, Johannesburg. Project background © The Southern African Institute of Mining and Metallurgy, 2008. SA ISSN 0038–223X/3.00 + The conveyor belt system used at 4 Belt, 0.00. Paper received Feb. 2008; revised paper Lonmin, consists of four conveyor belts received Mar. 2008.
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Increasing efficiency of conveyor belt transporting system 4 Belt Lonmin
Methodology Information collected
The necessary information about the conveyor belt system Information about the conveyor belt system currently in use used at 4 Belt was collected in order to determine the design at 4 Belt was collected to determine the design capacity of the capacity of the conveyor belt system. system. The design capacity of the conveyor belt transporting The information needed was collected by means of: system needed to be determined as part of the attempt to ➤ Underground observation achieve the objective mentioned earlier. ➤ Engineering drawings Table A1 shown in Appendix A, presents information ➤ Conveyor belt manuals about the conveyor belt transporting system that was ➤ Calculations. gathered by observation underground, observation from engineering drawings and performing the necessary In order to determine the amount of rock that needs to be calculations. Table I below presents a summary of the transported by the conveyor belt system, the monthly information about the conveyor belt system in production target for the mine had to be determined. The Appendix A. monthly production target was then divided into production Information about the vibratory feeders used to feed reef target per day for the mine in order to determine the amount and waste to the conveyor belt system was received from of rock that needs to be transported out of the mine on a Joest, the original supplier of the vibratory feeders, and was daily basis. compiled in Table A2, also shown in Appendix A³. The design capacity of the conveyor belt system was Table A1 in Appendix A, shows the different character- calculated from the information collected using different istics of the current conveyor belt transporting system, which methods of calculation. Three different methods of calculation include information on the different conveyor belt drive were used to determine the design capacity of the conveyor systems used, the support structure implemented and the belt system. The three different methods each considered dimensions and type of conveyor belt used. different aspects of the conveyor belt and were conducted in Table I shows the characteristics of the rock to be order to obtain the most accurate results. transported by the conveyor belt system. Added to the rock In order to determine the daily time available for rock characteristics is the assumed moisture factor of the rock to transport by the conveyor belt system, the hoisting times for be transported by the conveyor belt system. The moisture the conveyor belt system over a period of six months were factor influences the capacity of the conveyor belt since the compiled. From the hoisting times compiled an average water present in the broken rock adds to the mass of material hoisting time per day could be calculated for the to be transported. transportation of rock out of the mine. A demonstration of the conveyor belt system used at 4 After determining the design capacity of the conveyor belt Belt, Lonmin is shown in Figure 1. Figure 1 shows the system, the amount of rock needed to be transported per day individual conveyor belts (labeled R2, R1, R1A and R1B) that by the conveyor belt system and the daily time available for are part of the conveyor belt system used at 4 Belt and the the transportation of rock, various options for increased main ore passes allocated to the different working levels on efficiency of the conveyor belt system can be assessed. the mine. The options assessed for increasing the efficiency of the conveyor belt system were: Production target for 4 Belt ➤ Variation of the conveyor speed ➤ Concurrent tipping from two ore passes on the belt To establish the amount of ore that needs to be transported ➤ Increase the available drive unit power out of the mine, the monthly production target for a typical ➤ Increasing the feed rate from vibratory feeders twenty-three-shift month was calculated. The monthly ➤ Change in belt width/belt specifications. production target was then divided into a daily production
Table I Conveyor belt system data (summary)
Conveyor system data R1 Conveyor R1A Conveyor R1B Conveyor R2 Conveyor
Belt width 1.2 m 1.2 m 1.2 m 1.2 m Belt speed 1.5 m/s 1.5 m/s 1.5 m/s 1.5 m/s Belt length 804 m (slope) 442m (slope) 500 m (slope) 582.2 m (slope) Belt capacity 770 t/h 960 t/h 850 t/h 720 t/h Inclination 12º 12º 12º 12º
Rock characteristics UG2 Merensky Waste
In situ density 3.91 t/m3 3.17 t/m3 1.8 t/m3 Material size 300 * 350 mm 300 * 350 mm 300 * 350 mm Moisture factor 10% 10% 10% ▲ 190 APRIL 2008 VOLUME 108 NON-REFEREED PAPER The Journal of The Southern African Institute of Mining and Metallurgy SAIMM_09-20:Template Journal 5/7/08 7:59 AM Page 191
Increasing efficiency of conveyor belt transporting system 4 Belt Lonmin J o u r n a l
P a p e r
Figure 1—Graphic representation of the conveyor belt system4
target and later into production target per shift as the mine is Density (UG2) = 3.91 t/m³/density (Merensky) = 3.17 t/m³ operating in three shifts of eight hours each. The daily production targets from all operating levels were determined The valuation department at Lonmin gave the in situ density but cannot be displayed as it is a matter of confidentiality. for the UG2 Reef and Merensky Reef excavated at 4 Belt, as Since the reef and waste to be transported include a 3.91 t/m³ and 3.17 t/m³ respectively6. In the determination of certain amount of water, a moisture factor needed to be taken the belt capacity the in situ density has to be converted to a into account. A percentage of 10% by weight was allowed for loose density. The conversion has to be done by taking a moisture included in the rock to be transported. swell factor into consideration. A swell factor of 0.6, obtained It was determined that the production target for UG2 Reef from the valuation department at Lonmin, was used in the is far more than that of Merensky Reef with the UG2 determination of the loose density for both UG2 Reef and production target from level nine being the highest of the Merensky Reef transported6. individual levels on the mine. This implies that the biggest Shown in Table II is the difference in capacity for the problem with the so-called ‘bottleneck’, described earlier in conveyor belt system when transporting the two different reef this report, will occur at level nine. types (UG2 and Merensky) excavated at the mine. The results shown in Table II, however, do not take account of the drive units installed on the conveyor belt system and are purely Capacity of the system of electrical interlocked done to illustrate how the capacity of the conveyor belt conveyor belts system changes with the difference in the rock density to be transported. The capacity of each conveyor belt in the system was Parameters used in the determination of the belt capacity: calculated using different methods. Different methods of W = 1.2 m calculation were used to obtain the best results as each SF = 0.6 method takes different aspects of the conveyor belt system into consideration. For example, the design capacity of the V = 1.5 m/s conveyor belt (without taking consideration of the drive A = 0.0649 m² units) was found to be 828 t/h but when the drive units of the belt were taken into account, the capacity of the conveyor belt system was found to be only 721 t/h.
Capacity of the conveyor belt system, without Table II considering the drive units Conveyor belt system capacity for different reef In this section, the capacity of the conveyor belt system was types determined for both reef types mined at 4 Belt. The calculations performed in this section do not consider the UG2 Merensky existing drive units. Different rock densities were used in the In situ density (t/m³) 3.91 3.17 calculation of the capacity of the conveyor belt system since Loose density (t/m³) 2.35 1.9 the conveyor belt system is used for all rock transport out of Load (t/m) 0.153 0.123 Capacity (t/h) 828 666 the mine.
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Increasing efficiency of conveyor belt transporting system 4 Belt Lonmin
Capacity of the conveyor belt system, taking the then used in the calculation of the different power existing drive units into consideration requirements for each of the conveyor belts in the system of electrical interlocked conveyor belts. In this section, the capacity of the four conveyor belts was Since the shaft power for each driving unit could be found calculated taking the power output from the existing drive in the original design of the system, a factor of safety could units into consideration. The capacities of all four of the be calculated for a constant feed rate of 600 t/h to the system. electrical interlocked conveyor belts in the system were A feed rate of 600 t/h to the conveyor belt system was chosen calculated since the conveyor belt with the lowest capacity since it will be used later in this report. A feed rate of 600 t/h would act as a restraining factor to the amount of broken also allows a minimum factor of safety of 1.27. rock to be transported by the system of electrical interlocked The following section presents the tabulated results conveyor belts. obtained from the tension/power calculations performed with Results of capacity calculations, taking the drive units into a constant feed rate to the conveyor belt system of 600 t/h. consideration From Table III and Figure 2 it can be seen that when the drive Results of tension/power calculations unit power available is brought into account, the R2 conveyor In Table IV below, a summary of the tension/power belt has the smallest capacity of 721 t/h. Since all the calculations can be seen. Included in the summary is a conveyor belts operate in a closed system, the weakest of the calculated factor of safety for each conveyor belt when conveyor belts needs to be considered when determining the operating at a feed rate of 600 t/h. capacity for the system. The capacity for the belt conveyor system was calculated to be 828 t/h for the transportation of UG2 Reef and 666 t/h Capacity (t/h) for the transportation of Merensky Reef. The calculations performed earlier do not take the drive unit power available into account; therefore the maximum capacity for the current system will be taken as 721 t/h for the transportation of UG2 Reef and 666 t/h for the transportation of Merensky Reef.
Belt tensions and power requirements Tons per hour The belt tensions were determined for the three electrical interlocked conveyor belts. The different belt tensions for Conveyor Conveyor Conveyor Conveyor each of the electrical interlocked conveyor belts were determined using a constant feed rate of reef or waste to the Figure 2—Conveyor belt system capacities (derived from motor power belt of 600t/h. The calculated conveyor belt tensions were calculations)
Table III Conveyor belt system capacities (derived from motor power calculations)
R1 Conveyor R1A Conveyor R1B Conveyor R2 Conveyor
Mass of belt (kg/m) 36.2 36.2 36.2 36.2 Length of conveyor (m) 804 442 500 582 Inclination (degrees) 12 12 12 12 Shaft power (kW) 436 296 296 296 Belt speed (m/s) 1.5 1.5 1.5 1.5 Friction 0.04 0.04 0.04 0.04 Height component (m) 167 92 104 121 Capacity (t/h) 771 960 844 721
Table IV Power requirements (capacity—600 t/h)
R1 Conveyor R2 Conveyor R1A Conveyor R1B Conveyor
Load mass per metre 111.2 kg/m 111.2 kg/m 111.2 kg/m 111.2 kg/m Mass of moving parts 71 kg/m 71 kg/m 71 kg/m 71 kg/m Adjusted length 477.2 m 355.2 m 278.1 m 310 m Tension required to move empty belt 11 621.25 N 8 650.19 N 6 772.57 N 7 549.43 N Tension required to move load 20 801.34 N 15 483.31 N 12 122.49 N 13 513.02 N Tension required to lift load 182 207.87 N 131 860.96 N 100 148.94 N 113 335.04 N Total effective tension 214 630.46 N 155 994.46 N 119 044 N 134 397.49 N Slack side tension 14 809.50 N 10 763.62 N 8 214.04 N 9 273.43 N Sag tension 7 491.49 N 7 491.49 N 8 323.88 N 8 323.88 N Maximum belt tension 229 439. 96 N 166 758.08 N 127 367.88 N 143 670.92 N Power required 321.946 kW 233.992 kW 178.566 kW 201.596 kW Power available 436 kW 296 kW 296 kW 296 kW Factor of safety 1.35 1.27 1.66 1.47 ▲ 192 APRIL 2008 VOLUME 108 NON-REFEREED PAPER The Journal of The Southern African Institute of Mining and Metallurgy SAIMM_09-20:Template Journal 5/8/08 1:30 PM Page 193
Increasing efficiency of conveyor belt transporting system 4 Belt Lonmin J In Table IV, it can be seen that all the conveyor belts will conveyor belt system was determined for the increased speed o be able to transport ore at a feed rate of 600 t/h with a factor by taking the belt dimensions alone into consideration. The u of safety of 1.27 or more. capacities of all four conveyor belts, acting in the system of electrical interlocked conveyor belts, were determined for the r Hoisting times increased speed by taking the drive units into consideration. n The hoisting times for six months that were collected from Tension calculations were used for the same purpose a the planned maintenance department at Lonmin were mentioned above. l compiled. This was done to determine the time that is Change in belt speed available for hoisting reef and waste on a daily basis. In Table V below, the results for the months from May 2006 to Increase belt speed by 20% October 2006 can be seen. From Table V, it can be seen that Speed = (1.5 m/s * 20%) + 1.5 m/s P an estimated minimum of sixteen hours are available daily = 1.8 m/s a for hoisting both reef and waste material. This minimum time Capacity calculation for conveyor belts used at no. 4 p available for hoisting was used throughout the report in the calculation of the efficiency for the system of interlocked inclined shaft (belt speed increased by 20%) e conveyor belts. The capacity of the system of conveyor belts was calculated r when operating at a speed of 1.8 m/s. A loose density of Available options to increase the efficiency of the 2.35 t/m³ and 1.90 t/m³ for UG2 Reef and Merensky Reef conveyor belt transporting system respectively was used in the calculation. The calculations The following options were assessed in increasing the performed in this section considered only the conveyor belt efficiency of the conveyor belt system: alone and not the existing drive units. Table VI presents the ➤ Variation of the conveyor speed results obtained from the increase in speed of the conveyor ➤ Concurrent tipping from two ore passes on the belt belt system. ➤ Increasing the available drive unit power Parameters used in the determination of the belt capacity: ➤ Increasing the feed rate from vibratory feeders W = 1.2 m ➤ Changing belt width/belt specifications SF = 0.6 V = 1.8 m/s Variation of the conveyor speed A = 0.0649 m² The efficiency of the conveyor belt system was calculated with an increase of 20% in the operating speed of the conveyors and then compared with the efficiency of the Table VI conveyor belt system when operating at the current speed of 1.5 m/s. Capacity of conveyor belt system at increased In an attempt to obtain the most accurate results, three speed (belt specifications) different methods of calculation were performed. The results of the calculations performed at the increased speed were UG2 Merensky then compared with the results of the current speed of In situ density (t/m³) 3.91 3.17 conveyors. The comparison between the capacity results Loose density (t/m³) 2.35 1.9 obtained from the increased speed and those from the current Load (t/m) 0.153 0.123 Capacity (t/h) 990 796 speed can be observed in the next section. The capacity of the
Table V Total hoisting times
R 1 R1A R1B R 2 Month Total Total Budgeted Total Total Budgeted Total Total Budgeted Total Total Budgeted reef waste total reef waste total reef waste total reef waste total hoisting hoisting scheduled hoisting hoisting scheduled hoisting hoisting scheduled hoisting hoisting scheduled time time downtime time time downtime time time downtime time time downtime
May 14561 5716 9360 22245 5472 9360 16770 5117 9360 25622 5841 9360 June 24048 4037 9360 22981 4590 9360 19747 3999 9360 25327 4726 9360 Jul 24259 5800 10800 23419 4774 10800 17688 4740 10800 26584 4615 10800 Aug 28717 5367 10800 25494 4953 10800 18937 5890 10800 30928 5192 10800 Sep 24162 6090 10800 22249 5967 10800 16624 5930 10800 25853 5986 10800 Oct 20280 4353 3720 18664 4666 10440 14371 4183 10560 21471 4318 10440 Total 136027 31363 54840 135052 30422 61560 104137 29859 61680 155785 30678 61560 Average 22671 5227.17 9140 22508.7 5070.3 10260 17356 4976.5 10280 25964 5113 10260 h/month 377.85 87.12 152.33 375.14 84.51 171.00 289.27 82.94 171.33 432.74 85.22 171.00 h/day 16.43 3.79 6.62 16.31 3.67 7.43 12.58 3.61 7.45 18.82 3.71 7.43 h/day 20.22 19.98 16.19 22.53
Compiled from data received from the planned maintenance department at Lonmin 5
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Conveyor belt capacity calculations taking account of results obtained from the tension calculations performed for limited power available the conveyor belt system at the increased speed of 1.8 m/s. In the previous section, the motor power available was not Results of comparison between different belt speeds taken into account. In this section, the capacity for each In Table IX is the tabulated comparison of the effectiveness conveyor belt was calculated when operating at 1.8 m/s and between the two belt speeds of 1.5 m/s and 1.8 m/s. Table X account was taken of the limited motor power available. represents the results of the comparison between the two Table VII presents the results of the capacity calculations for different belt speeds using three different scenarios. the conveyor belt system at the increased speed when the From Figure 3, it can be seen that increasing the conveyor limited power available was brought into consideration. speed does not have a positive effect on the production ratio when the available motor power is taken into account. This Calculating the capacity for the conveyor belts operating outcome is the result of increasing power requirements by the at 1.8 m/s, taking the belt tensions into consideration conveyors for operation at a higher speed, which lead to the The capacity for each conveyor belt was calculated again, result that the conveyors can transport less ore when the now using the total effected tension on the belt when speed of the conveyors is increased due to the limited power operating at a speed of 1.8 m/s. Table VIII presents the supply available.
Table VII Capacity of conveyor belt system at increased speed (power)
R1 Conveyor R1A Conveyor R1B Conveyor R2 Conveyor
Mass of belt (kg/m) 36.2 36.2 36.2 36.2 Length of conveyor (m) 804 442 500 582 Inclination (degrees) 12 12 12 12 Shaft power (kW) 436 296 296 296 Belt speed (m/s) 1.8 1.8 1.8 1.8 Friction 0.04 0.04 0.04 0.04 Height component (m) 167 92 104 121 Capacity (t/h) 764 953 838 761
Table VIII Capacity of conveyor belt system at increased speed (tension)
R1 Conveyor R1A Conveyor R1B Conveyor R2 Conveyor
Load mass per metre (kg/m) 126.31 156.17 137.54 117.58 Total power available (kW) 436 296 296 296 Belt speed (m/s) 1.8 1.8 1.8 1.8 Effective tension (kN) 242.22 164.44 164.44 164.44 Capacity (t/h) 817 1011 890 761
Table IX Capacity at different speeds in tons/hour
R1 Conveyor R2 Conveyor R1A Conveyor R1B Conveyor 1.5 m/s 1.8 m/s 1.5 m/s 1.8 m/s 1.5 m/s 1.8 m/s 1.5 m/s 1.8 m/s
Taking account of belt alone 828 990 828 990 828 990 828 990 Taking account of motor power available 771 764 721 715 959 953 844 838 Taking account of tension on belt 908 817 768 761 1 018 1 011 897 890
Table X Vibratory feeders operating at 400 t/h (one box at a time)
UG2 time (min) Waste time (min) Merensky time (min) Total time (min) Total time (hour)
4 Level 84 2 5 Level 107 9 6 Level 90 7 7 Level 114 9 8 Level 66 8 9 Level 211 6 10 Level 16 28 Merensky waste 39 Merensky box 294 Total 688 108 294 1090 18.17 ▲ 194 APRIL 2008 VOLUME 108 NON-REFEREED PAPER The Journal of The Southern African Institute of Mining and Metallurgy SAIMM_09-20:Template Journal 5/8/08 1:43 PM Page 195
Increasing efficiency of conveyor belt transporting system 4 Belt Lonmin J From Figure 3 it can be seen that the capacities for all the 300 t/h will require a belt capacity of at least 600 t/h. Since o conveyor belts in the system are significantly increased at the the weakest of the conveyor belts in the interlocked system u increased speed when the available motor power is not taken hase a calculated capacity of 720 t/h, it will be able to handle into account. For the increase in speed of the conveyors to be a delivery rate of 600 t/h with a minimum factor of safety r utilized effectively, the installation of bigger drive units will of 1.27. n be necessary. Earlier in the report it was estimated that a minimum of a sixteen hours is available for daily hoisting. From Table X it l Concurrent delivering from more than one ore pass to can be seen that when feeding ore to the belt from only one the conveyor belt system ore pass at a time at the maximum vibratory feeder feeding The comparison was made between the times needed to rate of 400 t/h, eighteen hours may be needed for the transport ore when feeding from one ore pass and when transportation of the ore available according to the calculated P feeding from two ore passes concurrently. The idea behind daily production target. This may pose a problem since there a the concurrent feeding from more that one ore pass to the may be less time available for hoisting ore and then not all p conveyor belt system can be executed by the installation of a the ore available for hoisting will be hoisted for that day. simple automation program, allowing two chutes to be Referring to Table XI, two vibratory feeders are feeding e opened concurrently, that can be added to the system that is rock to the conveyor belt system concurrently at a rate of r already installed on the conveyor belt system or be controlled 300 t/h each. The problem described in the previous from the control room. paragraph is eliminated as less time than the minimum time Information compiled earlier in this report was used for available for hoisting is needed for the hoisting of the ore the comparison compiled in Table X and Table XI. Taking available on a daily basis. into consideration that the moisture factor was already In Table XI an example of a tipping schedule is given. The brought into account, it can be seen from Table X and Table idea behind the tipping schedule is to limit the amount of XI that ore can be transported more time efficiently when time needed to empty out all the ore passes. In Table XI, delivered to the conveyor belt system from two ore passes when looking at the UG2 tipping schedule, it can be seen that concurrently. This statement holds only when the vibratory the conveyor belt transporting system receives ore from levels feeders are operating at 75% utilization, delivering ore to the 4, 5 and 10 in sequence while level 9 is also delivering ore to conveyor belt system at a rate of 300 t/h each. Two ore the belt at the same time. This implies that less time is used passes delivering ore to the conveyor belt system at a rate of to empty out the ore passes. The concurrent delivering of ore Tons per hour 1.5 m/s 1.8 m/s 1.5 m/s 1.8 m/s 1.5 m/s 1.8 m/s 1.5 m/s 1.8 m/s
Figure 3—Capacity at different speeds
Table XI Vibratory feeders operating at 300 t/h (two boxes at a time)
UG2 UG2 Waste Waste Merensky Total Total time Tipping time (min) time (min) time (min) time (min) (min) (hour) (min) schedule
4 Level 112 Tip 3 Tip 5 Level 142 Tip 12 Tip 6 Level 120 Tip 10 Tip 7 Level 152 Tip 12 Tip 8 Level 88 Tip 11 Tip 9 Level 281 Tip Tip Tip 9 Tip 10 Level 22 Tip 37 Tip Merensky waste 52 Tip Merensky box 294 Tip Total 300 160 90 550 13 11 9 52 85 300 935 15.58
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to the conveyor belt transporting system allows ore to be Tabulated in Table XIII is the motor power requirements drawn from more than one level at a time, resulting in the for operating the various conveyor belts in the system of less time being wasted waiting for ore passes to be emptied conveyor belts for the range of capacities mention previously. out. The results obtained from Table XIII take account of a drive efficiency of 80%. Figure 5 represents a graph of the motor Increase the available drive unit power power requirements, using a drive efficiency of 80%. The graphs presented in Figure 4 and 5 were drawn for the Data were compiled of the belt power requirements needed for observation of the increase in motor power required as the each of the conveyor belts in the range of capacities between capacity increases. 500 t/h and 1500 t/h. A summary of the results for the range From Figure 5, it can be seen that the R1 conveyor belt of capacities mentioned in the previous example are shown in has the highest power requirements for all capacities. The Table XII, showing the belt power requirements for each of higher power requirements of the R1 conveyor belt are due to the ranges of capacities mentioned earlier. Figure 4 shows the the fact that the R1 conveyor belt covers the longest distance. relationship between the belt power requirements for Since the R1 conveyor belt has the highest power different capacities for each of the conveyor belts in the requirements, it will be one of the main deciding aspects system. when looking at the increasing of the drive unit power.
Table XII Summary of belt power requirements (kW)
Capacity (t/h) R1 Conveyor R2 Conveyor R1A Conveyor R1B Conveyor
500 271 197 150 170 600 322 234 179 202 700 373 271 207 233 800 423 308 235 265 900 474 344 263 297 1000 525 381 291 328 1100 576 418 319 360 1200 626 455 347 392 1300 677 492 375 424 1400 728 529 403 455 1500 779 566 431 487
Table XIII Summary of motor power requirements (kW)
Capacity (t/h) R1 Conveyor R2 Conveyor R1A Conveyor R1B Conveyor
500 339 246 188 212 600 402 292 223 252 700 466 339 258 292 800 529 385 293 331 900 593 431 328 371 1000 656 477 364 411 1100 720 523 399 450 1200 783 569 434 490 1300 847 615 469 529 1400 910 661 504 569 1500 973 707 539 609 Power (kW) 500 600 700 800 900 1000 1100 1200 1300 1400 1500 Capacity (t/h)
Figure 4—Belt power requirements ▲ 196 APRIL 2008 VOLUME 108 NON-REFEREED PAPER The Journal of The Southern African Institute of Mining and Metallurgy SAIMM_09-20:Template Journal 5/7/08 7:59 AM Page 197
Increasing efficiency of conveyor belt transporting system 4 Belt Lonmin J Increasing the feed rate from vibratory feeders The method of concurrent tipping from two ore passes o will also result in the added advantage that the amount of ore u According to information received from Joest, the suppliers of in ore passes from two levels will be reduced concurrently, the vibratory feeders used at 4 Belt, the feeding rate on the thus creating space for ore to be delivered to these ore r current vibratory feeders cannot be increased as the passes, resulting in more fluent operation conditions on the n maximum capacity motors available for the existing feeders different levels themselves. a are already installed. In the opinion of Mr. Ben Wessels at When comparing the option of concurrent tipping with l Joest, the installation of bigger vibratory motors will require the other options available, it can be clearly seen that all the major adjustments to the existing feeders and may lead to other options available require more adjustments to the premature destruction of the feeders3. already existing system than the option of concurrent tipping. Therefore, the option of concurrent tipping is preferable to P Changes in belt width/belt specifications the other available options since all adjustments made to the a system will cause more significant downtime for the instal- The capacity for the conveyor belt system can also be lation of bigger drive units, wider belts, bigger size idlers, p increased by increasing the width of the conveyor belt. An changes in structure, etc. than the installation of a simple e increase in the width of the conveyor belts will allow an automation program on the chutes from the ore passes that increase in the area available for loading rock, which in turn r can be run from the control room. . will result in a higher capacity. From the report it can be seen the option of concurrent With the increase in width of the conveyor belts, the tipping would decrease the time necessary to empty out all structure will require major modifications since the idlers the ore passes and therefore increase the efficiency of the currently installed on the structure will have to be replaced conveyor belt transporting system. A more efficient conveyor and the driving power must also be increased7. This option belt transporting system will ensure more fluent mining seems to be the least favourite of the five options due to all operations since the limited surge capacity will be utilized the modifications that needs to be done. The modifications to more effectively. the structure and drive units will have higher cost implications than any of the other options available, not to Recommendations mention the downtime involved on the operating shaft. The initial design of a mine or shaft is important. The shaft Conclusions must be designed for the maximum production rate that may be achieved through the life of the shaft. The particular The purpose of the project was to assess various options that scenario of 4 Belt shows that a shaft must consist of could increase the efficiency of the conveyor belt transporting adequate surge capacity to prevent the occurrence of system that is used at 4 Belt. Five options were explored: ‘bottlenecks’ in the ‘ore path’ out of the mine. If adequate ➤ Variation of the conveyor speed surge capacity were not provided in the initial design of the ➤ Concurrent tipping from two ore passes on the belt shaft, the situation that is experienced at Karee Belt is likely ➤ Increasing the available drive unit power to occur. Since the creation of additional surge capacity is ➤ Increasing the feed rate from vibratory feeders nearly impossible on an operating shaft, the transportation ➤ Changing belt width/belt specifications. system used needs to be altered. All alterations to the The preferred option was the concurrent tipping from two transportation system used in an operating shaft will cause or more ore passes to the conveyor belt system. The reason significant downtime in the shaft and therefore loss of for this statement is that if ore can be delivered from the ore production, which should be avoided at all costs. If passes to the belt system according to the schedule shown in alterations to the transporting system are necessary, the Table XI, less time will be needed to empty out all the ore option that would cause the least amount of downtime in the passes. operating shaft should be chosen. Power (kW) 500 600 700 800 900 1000 1100 1200 1300 1400 1500 Capacity (t/h)
Figure 5—Motor power requirements
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Increasing efficiency of conveyor belt transporting system 4 Belt Lonmin
References 4. KLEYNHANS, A. Mechanical Foreman, Karee 4 Belt, Lonmin Platinum, conversation with the author, Dec 2006. 1. MITCHELL, J. Shaft Engineer, 4 Belt, Lonmin, conversation with the author, 5. Planned Maintenance Department, Lonmin Platinum, Dec 2006. Dec 2006. 6. Valuation Department, Lonmin Platinum, Dec 2006. 2. REILY, D. Section Engineer, Lonmin Platinum, conversation with the 7. REZNICHENKO, G.G. MINN 308 Course Notes, University of the author, Dec 2006. Witwatersrand, Johannesburg, 2006. 3. WESSELS, B. Service Technician, Joest, [email protected], Dec 2006. 8. Dunlop Industrial Products, Conveyor Belt Manual, Dec 2006. ◆
Appendix A Conveyor belt system information
Table A1 Conveyor belt system information
Conveyor system data R1 Conveyor R1A Conveyor R1B Conveyor R2 Conveyor
Belt type Steel core Steel core Steel core Steel core Belt tension 215 kN 120 kN 135 kN 156k N Belt width 1.2 m 1.2 m 1.2 m 1.2 m Belt speed 1.5 m/s 1.5 m/s 1.5 m/s 1.5 m/s Belt length 804 m (slope) 442 m (slope) 500 m (slope) 582.2 m (slope) Belt mass 36.2 kg/m 36.2 kg/m 36.2 kg/m 36.2 kg/m Belt capacity 770 t/h 960 t/h 850 t/h 720 t/h Operation time 16 h 16 h 16 h 16 h Operating capacity 600 t/h 600 t/h 600 t/h 600 t/h Deviation 1.28 1.6 1.42 1.2 Capacity per day 9600 t 9600 t 9600 t 9600 t Inclination 12º 12º 12º 12º
Belt drive system R1 Conveyor R1A Conveyor R1B Conveyor R2 Conveyor
Belt drive type Triple Double Double Double Power 3 * 185 kW 2 * 185 kW 2 * 185 kW 2 * 185 kW Shaft power 436 kW 296 kW 296 kW 296 kW Speed (RPM) 1485 1485 1485 1485 Pulleys Drive pulleys Pulley diameter 900 mm 900 mm 900 mm 900 mm Pulley face width 1350 mm 1350 mm 1350 mm 1350 mm Head pulleys Pulley diameter 900 mm 900 mm 900 mm 900 mm Pulley face width 1350 mm 1350 mm 1350 mm 1350 mm Snub pulleys Pulley diameter 630 mm 630 mm 630 mm 630 mm Pulley face width 1350 mm 1350 mm 1350 mm 1350 mm Tail pulleys Pulley diameter 630 mm 630 mm 630 mm 630 mm Pulley face width 1350 mm 1350 mm 1350 mm 1350 mm Bend pulleys Pulley diameter 630 mm 630 mm 630 mm 630 mm Pulley face width 1350 mm 1350 mm 1350 mm 1350 mm Take-up pulleys Pulley diameter 630 mm 630 mm 630 mm 630 mm Pulley face width 1350 mm 1350 mm 1350 mm 1350 mm Number of pulleys 15 13 13 13 Pulley lagged Yes Yes Yes Yes Snub pulleys 2 2 2 2 Belt rap angle 450 450 450 450 ▲ 198 APRIL 2008 VOLUME 108 NON-REFEREED PAPER The Journal of The Southern African Institute of Mining and Metallurgy SAIMM_09-20:Template Journal 5/7/08 7:59 AM Page 199
Increasing efficiency of conveyor belt transporting system 4 Belt Lonmin J Appendix A (continued) o Conveyor belt system information u r Support system n R1 Conveyor R1A Conveyor R1B Conveyor R2 Conveyor a Structure Idler diameter 127 mm 127 mm 127 mm 127 mm l Idler length 450 mm 450 mm 450 mm 450 mm Idler spacing 0.9 m 1 m 1 m 0.9 m Idler angle 35º 35º 35º 35º Impact idlers No Yes Yes No P Return idlers V - Return V - Return V - Return V – Return a Diameter 12.7 cm 12.7 cm 12.7 cm 12.7 cm Length 63.5 mm 63.5 mm 63.5 mm 63.5 mm p Spacing 3 m 3 m 3 m 3 m e Angle 10º 10º 10º 10º r Rock characteristics UG2 Merensky Waste
In situ density 3.91 t/m3 3.17 t/m3 1.8 t/m3 Material size 300 * 350 mm 300 * 350 mm 300 * 350 mm Moisture factor 10% 10% 10%
Table A2 Vibratory feeder characteristics
Material Platinum ore Max lump size 500 mm Feed rate 400 tph Bulk density 2.4 t/m 3 Moisture 10% Abrasiveness Medium high Fed from Ore pass chute Feeding to Belt conveyor Liner material 10 mm Bennox
From [email protected]³
Dave Rankin retires as chairman of the Centennial Trust
University of the Witwatersrand. These funds were used to t the end of 2007 Dave Rankin, a very well-known establish the Trust, which allowed the creation of the figure in the Centennial Chair of Rock Engineering in the School of mining industry, A Mining Engineering, University of the Witwatersrand, retired as Chairman of the Johannesburg. Board of Trustees of the The first Centennial Professor appointed was Professor Centennial Trust. The Ugur Ozbay, in 1999, and he was succeeded by Professor photograph shows Dick Stacey in 2000. Professor Stacey will retire at the end of Professor Huw Phillips presenting a gift to Dave 2008, and it is expected that his replacement will be Rankin in appreciation of appointed during the course of this year. his contribution to the The Centennial Trust has allowed a strong rock Trust over a period of 10 engineering teaching and research capability to be continued years. at Wits University, and the control exercised by Dave Rankin The Centennial Trust at the University of the in managing the Trust is very sincerely appreciated. The Witwatersrand was established in 1996 from funds importance of the funding provided by the mining industry contributed by South African mining companies. The to establish the Trust is also acknowledged with occasion for the raising of the funds was to celebrate the appreciation. centenary of the establishment of the South African School Dr John Cruise has been elected as the new Chairman of the of Mines in 1896, which subsequently became the Board of Trustees of the Centennial Trust.
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